In the variety of display technologies, liquid crystal display (LCD) is widely accepted as a mature technology. In an LCD, the electro-optical effect of the liquid crystal is utilized to control the transmission and reflectivity of the liquid crystal unit by adjusting the electric circuit. Therefore, the intensity of the light emitted from the backlight module and passing through the color layer can be adjusted to achieve a different gray scale and the different colors of the image display. The backlight module is the most important component in an LCD for providing light.
In order to maintain a high quality display (the same brightness, uniformity, viewing angle, etc.), it is very necessary to use new backlight technologies to achieve a lower cost backlight module while enhancing the competitiveness of the product.
For improving the material efficiency of each portion, the light emitting diode (LED) as a backlight occupies an important part. If the LED can be driven in the same current and voltage while only changing or improving the internal structure or the arrangement of LED chip and the phosphor powder to enhance the luminous efficiency, then the above-described goal of reducing costs can be achieved. In addition, it is also possible to achieve cost reduction for the entire module by optimizing the coordination of the LED spectrum and the TFT (Thin-Film Transistor) penetrating spectrum to reach the same white point chromaticity, and then cooperating with the above-mentioned ways to improve the efficiency of LED.
White LED is currently used in LCD backlight modules, which is formed by mixing the blue light emitted from blue chips and the yellow light emitted from stimulated YAG (yttrium aluminum garnet)/Silicate/Nitrides (NOx) phosphor powder and a white light is presented in the human eyes.
For the LED applied to an LCD backlight module, because it is necessary to meet the NTSC color gamut established by National Television Standards Committee, the blue light of an LED usually requires a shorter wavelength. The current blue chip of an LED applied to an LCD backlight module usually has a peak wavelength (Wp) emitted by blue chips in the range of 440-445 nanometers (nm) and the dominant wavelength (Wd) of the corresponding spectrum in the range of 444-452.5 nanometers (nm), the conversion of Wd and the Wp is related to FWHM (Full Width of Half Maximum) of the blue chip chromatography.
However, the LED has greater efficiency while the Wp is at the long wavelength. From the viewpoint of the brightness, when the ratio of energy passed into the human eyes in the visual function is increasing, the brightness of the LED will be promoted. In addition, the exciting efficiency of YAG phosphor powder is different from the excitation wavelengths of different sources, in general, the best excitation wavelength is about 450 nanometers (the YAG from different suppliers or made of different components may has a slightly different excitation spectrum). When the Wp shifts from 440 nm to 450 nm continuously, the efficient excitation energy of the YAG can be calculated by the excitation spectrum of the YAG phosphor powder and will be increasing. Finally, after Wp red-shifting, the light emitted from the LED is absorbed by the backlight unit (LGP, diaphragm), the spectrum of the emitted blue light has the increased brightness ratio. Equally, the brightness ratio is continuously increasing after the light passes the TFT so that the NTSC color gamut of the LCD module presents an increased ratio of blue light and the whole module outputs a bluish light. Therefore, it is necessary to adjust the NTSC color gamut back to the original color gamut.
Therefore, it is necessary to provide a white light emitting diode to solve the problems existing in conventional technologies, as described above.